1. Field of the Invention
The present invention relates to a method of manufacturing a nozzle plate, and a liquid ejection head and an image forming apparatus comprising the nozzle plate, and more particularly, to technology for forming a liquid-repelling film onto the surface of a nozzle plate in which a plurality of microscopic liquid ejection ports (nozzles) for ejecting liquid are formed, and to a liquid ejection head and an image forming apparatus using this nozzle plate.
2. Description of the Related Art
An inkjet recording apparatus or inkjet printer is known as an image forming apparatus. The inkjet printer comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) for ejecting ink (liquid), and forms images on a recording medium by ejecting droplets of the ink from the nozzles while causing the inkjet head and the recording medium to move relatively to each other.
Various methods are known as ink ejection methods for an inkjet recording apparatus. For example, a piezoelectric method is known, in which a diaphragm which constitutes a portion of a pressure chamber is deformed by the deformation of a piezoelectric element, thereby changing the volume of the pressure chamber, ink is introduced into the pressure chamber from an ink supply passage when the volume of a pressure chamber is increased, and the ink inside the pressure chamber is ejected from the nozzle in the form of ink droplet when the volume of the pressure chamber is decreased.
In an inkjet recording apparatus of this kind, if a liquid-repelling or ink-repelling treatment is not provided on the surface of the nozzle plate in which the nozzles of the inkjet head are formed, then ejection abnormalities, such as bending of the direction of flight of the ink droplets ejected from the nozzles may occur, due to ink adhering to the periphery of the nozzles on the surface of the nozzle plate.
On the other hand, if a liquid-repelling film is formed on the surface of the nozzle plate, then soiling around the periphery of the nozzles can be removed more readily, leakage of ink from the nozzles is reduced, and the direction of ejection of the ink and the ink ejection volume can be stabilized. However, in this case, if the formation of the liquid-repelling film is not uniform in the periphery of the nozzles on the surface of the nozzle plate, then ejection abnormalities such as bending of the flight will still occur.
Various methods have been proposed for forming a liquid-repelling film uniformly to a high degree of accuracy at the periphery of the nozzles on the surface of the nozzle plate. One method for forming a liquid-repelling film uniformly at the periphery of the nozzles is a method which forms a liquid-repelling film by introducing a filling material into the nozzles before forming the liquid-repelling film on the surface of the nozzle plate, in such a manner that the liquid-repelling film does not enter into the nozzles. In this case, there is a method which bonds a sheet (covering material) that covers the nozzle apertures onto the surface of the nozzle plate when the filling material is introduced, and a method which does not bond such a sheet.
For example, Japanese Patent Application Publication No. 8-309997 discloses a liquid-repelling film forming method in which the sheet is bonded. In the method, the whole surface of the nozzle plate (the ink ejection face) formed with nozzle apertures is covered with a dry film resist at first, ultraviolet light is then irradiated from the rear face of the nozzle plate, in such a manner that only the portions of the dry film resist covering the nozzle apertures become insoluble with respect to a developer, whereupon a filling material is introduced from the rear face of the nozzle plate, and the rear face of the nozzle plate and the interior of the nozzle apertures are covered with the filling material. Thereupon, the dry film resist is developed, the portion of the dry film resist on the surface of the nozzle plate other than the portions covering the nozzle apertures are removed, a liquid-repelling film is formed on the portion of the surface of the nozzle plate other than the regions of the nozzle apertures, and finally, the dry film resist remaining on the regions of the nozzle apertures is removed along with all of the filling material, thereby yielding a nozzle plate in which the liquid-repelling film is formed on the surface of the nozzle plate apart from over the nozzle apertures.
Japanese Patent Application Publication No. 9-76492 discloses a liquid-repelling film forming method in which no sheet is bonded. In the method, a dry film resist is filled into nozzle apertures formed in a nozzle plate, the surface of the nozzle aperture sections on the nozzle plate is cut away by etching, and the dry film resist of the nozzle aperture sections is caused to project at the surface of the nozzle aperture sections. A surface treatment layer (liquid-repelling film) is then formed on the surface of the nozzle aperture sections other than the nozzle apertures, and the dry film resist is removed, thereby yielding a nozzle plate formed with a liquid-repelling film on the surface other than the nozzle apertures.
Japanese Patent Application Publication No. 2000-108359 discloses a liquid-repelling film forming method in which the sheet is bonded. In the method, a transparent masking sheet is bonded as a covering material onto the surface of a nozzle plate in which nozzles are formed (the surface on the side of the nozzle aperture sections), and a filling material or an ultraviolet-curable adhesive having properties of repelling an ink-repelling resin film solution is filled from the opposite side. The ultraviolet-curable adhesive is cured by irradiating ultraviolet light from both sides, and the masking sheet on the nozzle surface is removed. Then, an ink-repelling resin film solution is applied onto the nozzle surface, dried and heated, thereby forming an ink-repelling resin film. Finally, the ultraviolet-curable adhesive filled in the nozzles is removed, thereby yielding a nozzle plate formed with an ink-repelling film on the nozzle surface thereof.
However, if a filling material for preventing liquid-repelling film from entering into the nozzle apertures is filled into the nozzles, then in the case of a method where no sheet is bonded onto the nozzle surface of the nozzle plate, the filling material projects from the nozzles, and it can be expected that this projection will not be uniform, and hence the liquid-repelling film will not be uniform, either. For example, in the method described in Japanese Patent Application Publication No. 9-76492, if the dry film resist is made to project from the nozzle apertures by cutting the surface of the nozzle plate, then there is a loss of homogeneity within the plane of the surface of the nozzle plate, and the subsequently formed liquid-repelling film will have variations between the respective nozzles.
Moreover, in a method where a sheet is bonded onto the nozzle surface when the filling material is filled into the nozzles, when the filling material is introduced into the nozzles, gas remains inside the nozzles, giving rise to uneven filling of the filling material, and hence it is expected that the liquid-repelling film will also lack uniformity. For example, in the methods described in Japanese Patent Application Publication Nos. 8-309997 and 2000-108359, uniform filling is not achieved when the filling material is introduced into the nozzles, and hence the liquid-repelling film is not uniform. Furthermore, in the case of Japanese Patent Application Publication No. 8-309997, in particular, a step of developing the dry film resist is required, and hence the process is troublesome.